It sounds like you are in a nice spot where you have options moving forward with investing, (congrats).

You have options!

Monetary- they need to bring $XXXXX amount of cash in or monthly sources of income. 

Your best option would be to refinance your loan (if any) and get a construction loan for the improvements.

Since I'm a new immigrant with no credit score, a DSCR with 30-35% down payment is my only option, so the 50K need to include that down payment alongside all other costs (closing, rehab, etc). 

Do you have any recommendations on a lending source for a property such as this?

My client had some things come up that prevented her from executing, but these were some of the options I had put together for her, a regional bank, a regional CU, and a national bank.Reminder that NOI sizes CRE debt, and that's often what determines the down payment requirement, not anything to do with the client or particular lender, just the property itself.

Given the expected appreciation, what is your expected total return if you hold it over the next 5 years.Can you cover the large negative cash flow, turnover costs and maintenance from other sources?

This is not a great return, but not terrible.As others noted, there are other risks, like having the property insured at full replacement or purchase price, or if the option is 100% seller financing with no money down or very little, versus 20% traditional down payment, this can start to move it into a better investment.

I've found options in Costa Rica, but rates are in the 10% range.Does anyone have any experience or guidance on obtaining a mortgage equivalent to purchasing a 2nd home in the US?